How to fill vertices that have been traced with color
I presume you have been creating points connected by edges, but have not created any faces. 

Select the points (vertices) you want to connect and press F (to create a face). You can then assign a material to it and have that material be of any color of your choosing.

As a matter of precaution try not to create faces connected to more than 4 vertices.

Vertices and edges are not visible when rendered and cannot have materials, but faces can.